@timestamp for time zone issues

I have an old logstash docker image, its version is 6.2.2 and the time zone is +0800, my new logstash docker image version is 7.12.1 , the time zone is +0000, but there is a surprising result, the final output @timestamp value of the 6.2.2 version is +0000, while the 7.12.1 output @timestamp value is +0800, I do not understand why this is so? Here is my relevant logstash configuration

grok{
        match => {"message" => "\[%{TIMESTAMP_ISO8601:log_time}\] \[%{LOGLEVEL:level}\] \[%{DATA:thread}\] %{GREEDYDATA:class_name} %{NUMBER:line_num} \[%{GREEDYDATA:trace_id}\] - %{GREEDYDATA:content}"}
    }

date {
        match => ["log_time", "yyyy-MM-dd HH:mm:ss.SSS"]
    }